Optical transponder with equipment failure protection

ABSTRACT

A dual E/O transmitter module optical transponder comprising an E/O receiver module capable of converting an ingressing optical signal from an optical signal source to an electrical signal, a pair of E/O transmitter modules connected in parallel and each capable of converting the electrical signal to an egressing optical signal, a control device for enabling one of the pair of E/O transmitter modules and disabling the other of the pair of E/O transmitter modules, and an optical coupler coupled to the pair of E/O transmitter modules for feeding the egressing optical signal from the enabled E/O transmitter module to an optical signal destination.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part application of thecurrently co-pending U.S. application Ser. No. 10/271,770, filed Oct.17, 2002, which is a National Phase application of InternationalApplication Ser. No. PCT/IL01/00343 filed Apr. 15, 2001, whichInternational Application claims priority on Israel Application Ser. No.135,715 filed Apr. 18, 2000.

FIELD OF THE INVENTION

The invention is in the field of optical transponders.

BACKGROUND OF THE INVENTION

Optical ring networks include two optical fibers, one dedicated foradding and dropping working channels and the other dedicated forprotection channels. Optical ring networks typically include one or moreso called unidirectional optical transponders for adding an opticalsignal to a working channel or dropping one off therefrom, so called 1×2add direction optical transponders for adding identical optical signalsto the working channel and the protection channel, and so called 2×1drop direction optical transponders for dropping an optical signal fromeither the working channel or the protection channel.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a dual E/Otransmitter module optical transponder comprising:

-   -   (a) an O/E receiver module capable of converting an ingressging        optical signal from an optical signal source to an electrical        signal;    -   (b) a pair of E/O transmitter modules connected in parallel and        each capable of converting said electrical signal to an        egressing optical signal;    -   (c) a control device in communication with each E/O transmitting        module of said pair for maintaining their performance and for        enabling one of said pair of E/O transmitter modules and        disabling the other of said pair of E/O transmitter modules; and    -   (d) an optical coupler coupled to said pair of E/O transmitter        modules for feeding said egressing optical signal from said        enabled E/O transmitter module towards an optical signal        destination,    -   thereby the transponder keeping itself workable to provide the        egressing optical signal towards the destination, even in case        of non-satisfactory operation or failure of one of said E/O        transmitter modules.

The present invention presents a novel solution to the problem ofcessation of data transmission through a conventional unidirectional ordrop direction optical transponder having only a single E/O transmittermodule in the event of its equipment failure.

Further, the present invention presents a novel solution of an opticaltransponder with multi-stage equipment failure protection. Differentstages of the equipment protection are respectively ensured by thesecond E/O transmitter module, by the optical coupler connected to thepair of the E/O transmitter modules, by optionally using a pair of O/Ereceiver modules for producing two electrical signals, and by arranging(for at least one O/E receiver module) a branch of two parallel pathswhere an electrical signal is checked and monitored in the main path andjust conducted in a bypass path. The multi-stage equipment failureprotection is ensured by a single control device that controls thetransponder equipment. Essential features of the proposed opticaltransponder will become apparent from the following description and thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it can be carriedout in practice, preferred embodiments will now be described, by way ofnon-limiting examples only, with reference to the accompanying drawings,in which similar parts are likewise numbered, and in which:

FIG. 1 is a schematic representation of a dual E/O transmitter moduleunidirectional optical transponder; and

FIG. 2 is a schematic representation of a dual E/O transmitter moduleand dual O/E receiver module drop direction optical transponder.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a dual E/O transmitter module unidirectional opticaltransponder 10 including an optical to electrical (O/E) receiver module11 coupled to an optical signal source (not shown); a field programmablegate array (FPGA) control device 12; an electrical splitter 13; anelectrical selector 14 (constituting a switching device); a main path 16extending between the splitter 13 and the selector 14 and having a Clockand Data Recovery (CDR) unit 17, a demultiplexer 18, a Forward ErrorCorrection (FEC) and Performance Monitoring (PM) unit 19, and amultiplexer 21; a bypass path 22 (constituted by an electrical shunt)extending between the splitter 13 and the selector 14; a secondelectrical splitter 23; a pair of E/O transmitter modules 24 and 26connected in parallel, and an optical coupler 27 coupled to an opticalsignal destination (not shown).

The O/E receiver module 11 converts an ingressing optical signal to anelectrical signal, and provides an optical Loss of Signal (LOS) signalto the FPGA control device 12 in the event that no optical signal isdetected thereat. The splitter 13 splits an electrical signal from theO/E receiver module 11 into two identical signals which are respectivelyfed to the main path 16 and the bypass path 22. The CDR unit 17 performsclock and data recovery on an electrical signal, and provides a dataLoss of Signal (LOS) signal to the FPGA control unit 12 in the eventthat no data signal i.e. a stream of consecutive zeros is detectedthereat. The FEC and PM unit 19 performs forward error correction andperformance monitoring on an electrical signal, and provides a data Lossof Signal (LOS) signal, a Loss of Frame (LOF) signal, a Signal Fail (SF)signal, and a Signal Degrade (SD) signal to the FPGA control device 12as appropriate. The control device 12 is also responsible for monitoringperformance of the O/E transmitter modules 24 and 26. The selector 14can feed either an electrical signal from one of the main path 16 or thebypass path 22 to the splitter 23 as determined by an SX signal from theFPGA control device 12. Selection of the bypass path 22 can be caused bya fault in the main path 16, for example due to a signal loss, a failureof any of the signal handling units 17, 18, 19, 21, etc. The splitter 23splits the electrical signal to two identical signals which arerespectively fed to the E/O transmitter modules 24 and 26. The E/Otransmitter modules 24 and 26 are capable of being independently enabledby an TX_EN signal from the FPGA control device 12 and can each convertan electrical signal to an egressing optical signal which is fed to theoptical coupler 27. The E/O transmitter modules 24 and 26 provide TX_LOSsignals to the FPGA control device 12 in the event that they are enabledbut no optical signal is detected thereat.

In the default mode of operation of the optical transponder 10, the FPGAcontrol unit 12 switches the selector 23 to feed electrical signals fromthe main path 16 to the E/O transmitter module 24, and disables the E/Otransmitter module 26. In the case of an TX_LOS_1 signal from the E/Otransmitter module 24, it is disabled and the E/O transmitter module 26is enabled. The protection against equipment failure of the E/Otransmitter module 24 by the E/O transmitter module 26 is unaffected bythe position selection of the selector 23.

FIG. 2 illustrates another embodiment 30 of the optical transponder,comprising two O/E receiver modules RX that receive a first and a secondoptical signals and respectively convert thereof into a first and asecond electrical signals. The transponder 30 respectively comprises twosymmetric parallel branches for handling the first and the secondelectrical signals generated by the two O/E receiver modules. Each ofthese branches is similar to the branch of FIG. 1 that comprises paths16, 22 and a selector 14. Both of the parallel branches in FIG. 2 aremonitored by the transponder's common control device (in this example,FPGA). In addition to the functions of the transponder 10 shown in FIG.1, the transponder 30 is capable of selecting an electrical signal fromthose four ones available in the two parallel branches for furtherconverting the selected electrical signal into the optical form by anenabled E/O transmitter module. These control functions of the controldevice are implemented by a command SX_1 to a selector of the first(left) branch, a command SX_2 to the selector of the second (right)branch, and SX_3 to the central selector; the three selectors thusforming a combined switching device. If either of the two O/E receivermodules RX is faulty (i.e., any of them reports OPTICAL LOSS) to thecontrol device, the second of the branches is selected by the FPGA andthe transponder becomes equivalent to that shown in FIG. 1. If neitherof the receivers RX is faulty/malfunctioning, and neither of the signalhandling devices in both of the main paths reports about a problem, thecontrol device may compare the quality of the first electrical signal inthe first main path with the quality of the second electrical signal inthe second main path based on comparing and processing the servicesignals, for example those indicated in FIG. 2: DATA LOSS_1, DATALOSS_2, LOSS_1, LOSS_2, LOF_1, LOF_2, SF_1, SF_2, SD_1, SD_2. Thecontrol device may further select the electrical signal with a betterquality for further processing. The control device can be configured tooperate according to any pre-selected algorithm and/or a predeterminedsystem of defaults for deciding which of the four electrical signals isto be chosen in each specified situation for being fed to the enabledE/O transmitter module. At last, one of the electrical signals conductedvia the bypass paths can be selected. The illustrated transponder isthereby characterized by the multi-stage equipment failure protection,though also allows selecting a better quality signal if the equipment isin order. The dual E/O transmitter module optical transponder of FIG. 2is particularly suitable for implementation as a drop direction opticaltransponder.

While the invention has been described with respect to a limited numberof embodiments, it will be appreciated that many variations,modifications, and other applications of the invention can be madewithin the scope of the appended claims.

1. An optical transponder comprising: (a) an O/E receiver module capable of converting an ingressing optical signal from an optical signal source to an electrical signal; (b) a pair of E/O transmitter modules connected in parallel and each capable of converting said electrical signal to an egressing optical signal; (c) a control device in communication with each E/O transmitter module of said pair for monitoring their performance and for enabling one of said pair of E/O transmitter modules and disabling the other of said pair of E/O transmitter modules; and (d) an optical coupler coupled to said pair of E/O transmitter modules for feeding said egressing optical signal from said enabled E/O transmitter module towards an optical signal destination, thereby the transponder providing the egressing optical signal towards the destination.
 2. The transponder according to claim 1 and further comprising a second O/E receiver module for converting a second optical signal to a second electrical signal, and a switching device for switching one of said electrical signals to said enabled E/O transmitter module, wherein said control device is in communication with each of said two O/E receiver modules for detecting malfunction if takes place at any of them and for further controlling the switching device to block the electrical signal fed from the O/E receiver module being not in order, the transponder is thereby adapted to provide the egressing optical signal towards the destination in case of malfunction of one of said E/O transmitter modules and/or one of the O/E receiver modules.
 3. The transponder according to claim 1, comprising a main path and a bypass path for conducting said electrical signal in parallel from said O/E receiver module to a switching device, said main path comprising at least one signal handling unit in communication with said control device; the control device being operative to detect a malfunction if takes place in the main path and to select, for feeding to said enabled E/O transmitter module, either the electrical signal handled in said main path, or the electrical signal transmitted via said bypass path; the transponder thereby being adapted to keep itself workable to provide the egressing optical signal in case when at least one of the following equipment groups is not in order: one of said E/O transmitter modules; one of said O/E receiver modules; said at least one signal handling unit in the main path.
 4. The transponder according to claim 2, comprising a first main path and a first bypass path for conducting said first electrical signal in parallel from said first O/E receiver module to said switching device; the first main path comprising at least one signal handling unit for handling said first electrical signal, being in communication with said control device; the transponder also comprising a second main path and a second bypass path for conducting said second electrical signal in parallel from said second O/E receiver module to said switching device; the second main path comprising at least one signal handling unit for handling said second electrical signal, being in communication with said control device; said control device being operative to detect a malfunction and/or estimate a signal quality in the first and second main paths and select, for feeding to the enabled E/O transmitter module, one of the following four electric signals: the first electrical signal from the first main path, the first electrical signal from the first bypass path, the second electrical signal from the second main path, and the second electrical signal from the second bypass path; thereby the transponder, when being in a regular condition, allows selection of a better quality electrical signal to form the egressing optical signal, while remains workable to provide the egressing optical signal in case of a malfunction of one or more of the following equipment groups: one of said E/O transmitter modules; one of said O/E receiver modules, at least one of the signal handling units in one or both of said main paths.
 5. The transponder according to claim 1 wherein the control device is FPGA based.
 6. The transponder according to claim 3, wherein said at least one signal handling unit is selected from a list comprising a Clock and Data Recovery (CDR) unit, a Forward Error Correction (FEC) unit and a Performance Monitoring (PM) unit.
 7. The transponder according to claim 4, wherein said at least one signal handling unit is selected from a list comprising a Clock and Data Recovery (CDR) unit, a Forward Error Correction (FEC) unit and a Performance Monitoring (PM) unit. 